Reliable Data Acquisition Ensures Rail Car Safety

While manufacturers now perform computer simulations on all new rail car designs and modifications, they still perform on-track tests before releasing designs or modifications to production or to diagnose performance problems. The reason for this is that simulation is not 100% accurate, and the only way to really demonstrate that a design meets performance specifications is to perform an actual on-track test.

This is why on-track tests of most new vehicle designs are required for cars used in the North American Freight Service. To perform these tests, you measure forces, accelerations, and displacements at critical locations on the rail car being tested by installing a number of sensors at those locations. You then connect these sensors to a data acquisition system to record the values while running the car under test over a test track. Once the test run is complete, the measured values are analyzed to ensure that the rail car meets performance specifications.

Running these tests can be quite expensive. To help keep these costs under control, you need a data acquisition system that is reliable, accurate, easy to use, and will operate in adverse conditions. You do not want to re-run a test because your data acquisition system did not perform properly.

For a recent series of tests on a new truck trailer design, Sims Professional Engineers (SPE) of Highland, IN chose the SoMat eDAQ data acquisition system from HBM. According to Cody Kasten, an SPE engineer, the eDAQ was perfect for this application. Not only is the eDAQ rugged and reliable, it supports a wide variety of transducers and is easy to set up and operate.

Test Specs Are Demanding

The Association of American Railroads (AAR) standard M-1001, “Design, Fabrication, and Construction of Freight Cars” describes the tests to be performed and the required test conditions. This standard is in Section C, Part II of the AAR Manual of Standards and Recommended Practices.

Chapter XI, “Service-Worthiness Tests and Analyses for New Freight Cars,” of M-1001 specifies a number of certification tests including:

Hunting (vehicle lateral instability)

Constant curving

Spiral

Twist, roll

Pitch

Yaw, sway

Dynamic curving

Because this trailer was designed to not only be used on roads, but also to be transported on railroad tracks, it had to also meet the requirements for rail-compatible vehicles spelled out in Chapter IX of M-1001.

At the heart of the test system SPE devised for these tests are two SoMat eDAQ data-acquisition systems. Other components in the system included:

The eDAQs were mounted in weatherproof NEMA boxes attached to the transition flat car, as shown in the image. Ahead of the flat car is the engine which powers the system on rail. Attached to the flat car is the trailer and rail bogie being tested. In order for the trailer to be transported by rail, the trailer is attached to a bogie, which follows the trailer. One or more trailers with bogies may be attached to the train for testing purposes to simulate actual operation.

SPE used a number of different sensors to measure important parameters. Three vertical accelerometers were used to measure vertical excitation due to track perturbations, impacts or other phenomena. Three lateral accelerometers were used to determine if lateral accelerations met the requirements specified in Chapter XI.

To measure deflections, and ultimately determine the roll of the units and flat car, SPE used six potentiometers. The longitudinal load at the bogie hitch plate to trailer connection was determined using a specialized load pin. This data was used to determine the longitudinal loads through the system.

Finally, strain gages were applied to both the bogie and trailer. The locations for these strain gages were determined by doing a finite-element analysis of the design. SPE engineers identified fourteen particularly critical areas during this analysis, four on the trailer and ten on the bogie.

The SoMat eDAQs attached to the transition flat car

Quickly and easily configure the channels of the system with SoMat TCE software

Solar Panels Provide Portable Power

To power the system, SPE installed two SunWize SW90C solar panels on the flat car. The solar panels provide up to 90 W each. The solar panels charge a bank of three batteries, which is then connected to the data-acquisition system and ultimately powers it.

SPE decided to use solar panels instead of larger batteries for this test system because it was more cost-effective to use smaller batteries and it eliminated the need to replace batteries in adverse weather conditions. Some of the tests were run during the winter, and battery life is much shorter in colder weather.

The solar panels also eliminated the need to check battery capacity while running the test. They provided more than enough power to keep the batteries charged throughout the duration of the test. Using solar panels meant that having enough power was one less thing that SPE had to worry about.

Once the test system had been assembled, and technicians had put the sensors in place, SPE engineers used SoMat TCE software running on a laptop computer to program the system, as shown in the image. This software allowed the engineers to quickly and easily configure the channels of the system, including calibrations for each of the transducers. Once the setup was complete, they disconnected the computer and, the data acquisition system ran on its own.

The on-track testing took place on the Canadian Pacific Railroad tracks between St. Paul, MN and Superior, WI, a distance of about 150 miles. Over a period of about two weeks, SPE ran two unloaded trips and two loaded trips. Sensor readings were taken at a sample rate of 200 Hz. Despite being unattended, the test ran without a hitch, and the data acquisition system recorded between 2 and 4 Gigabytes of data on each run.

Data Analysis Was a Snap

Once the test was complete, SPE engineers once again connected a laptop to the eDAQ system and downloaded the raw test data for analysis. To analyze the data, SPE engineers used SoMat Infield. The first step was to filter the data digitally using a Butterworth filter with a 15 Hz cutoff frequency as specified in AAR M-1001. The purpose of filtering the data is to remove noise from the test data.

The final step in analyzing the test data was to look for strains, accelerations, and deflections that exceed the limits set by the AAR standard. This step was a snap using the statistics function of the SoMat Infield software. While the data analysis for this test was relatively simple, the Infield software is capable of more sophisticated analysis. It can, for example, not only identify maximum and minimum reading, but also calculate mean, standard deviation and rms values, as well as perform rainflow, time at level and frequency analysis.

After analyzing the data, SPE was pleased to report that the flat car/trailer/bogie combination passed the test. SPE prepared a report that included tables showing the maximum values recorded and compared those values to the values allowed by the AAR standard. Also shown was the margin of safety. This report was given to the client who then submitted the report and other documentation to the AAR and the Federal Railroad Administration for approval.

Throughout the process, Kasten noted, the tech support that HBM provided was a big help. Whether it be help using the hardware or software, “HBM tech support was always there when we needed them,” he said.